This invention relates to knock controls for spark ignited internal combustion engines of the type which sense knock and adjust an engine operating parameter such as ignition timing in order to prevent such knock from exceeding trace levels. Such systems are known in the art as shown in U.S. patents such as Harned et al U.S. Pat. No. 4,002,155, issued Jan. 11, 1977, West U.S. Pat. No. 4,106,477, issued Aug. 15, 1978, West et al U.S. Pat. No. 4,111,035, issued Sept. 5, 1978, Kearney et al U.S. Pat. No. 4,276,861, issued July 7, 1981 Chen et al U.S. Pat. No. 4,364,260, issued Dec. 21, 1982, Brandt U.S. Pat. No. 4,384,473, issued May 24, 1983, and Oh U.S. Pat. No. 4,424,706, issued Jan. 10, 1984. In addition, such systems have been produced on motor vehicles in this and other countries for a number of years.
Even the best of the prior art knock control systems are subject to the difficulty of sensing knock in the noisy engine environment and the dependence of those characteristics which distinguish knock from noise on certain engine structural and operating parameters which vary from one type of engine to another, from one engine to another and from one engine operating mode to another. Most systems that work well require design calibration of a number of calibration factors such as filter corner or center frequencies, amplifier gain factors or pulse shortening or lengthening factors, which increase the expense of the systems through increased development costs and a proliferation of inventory. In addition, such systems may not match all engines of a particular type or the full range of operating environments, particularly as engines age and their characteristics change.
An adaptive knock control would allow more flexibility in the design of such knock controls, with possibilities for reduced calibration requirements, reduced inventory and better operation over the life of the vehicles. Until recently, such adaptive knock control systems seemed too expensive and cumbersome to be seriously considered. However, the advent of programmable switched capacitor circuit technology has made such circuits a possibility to consider.